Rubber latex compositions and the manufacture of articles therefrom



May 7 1957 I a A. J. LOWE RUBBER LATEX COMPQSITEIJ NQ AND THE 2,791,567MANUFACTURE OF ARTICLES THEREFROM Filed April 23 1953 I200 I600 20002400 2800 3200 3600 4000 4400 AVERAGE MOLECULAR WEIGHT I I I I I l O O 8w 3 w 3 INVE N TOPJ fz/MJ 941M ATTORNEYS United States Patent RUBBERLATEX COMPOSITIGN S AND THE MAN U- FACTURE 0F ARTICLES THEREFRGM ArnoldJohn Lowe, Manchester, Donald Butler, Moston, Manchester, and ErnestGordon Coekbain, Welwyn Garden City, England, assignors, by mesneassignments, to Shell Development Company, New York, N. Y., acorporation of Delaware Application April 23, 1953, Serial No. 350,662Claims priority, application Great Britain April 25, 1952 9 Claims. (Cl.260-) This invention relates to rubber latex compositions and to themanufacture ofrubber articles therefrom.

In the manufacture of rubber articles from latex compositions the shapeof the article may be obtained by immersing a suitably shaped former inthe latex composition in the so-called dipping process, or by filling asuitably shaped mould with the latex composition as, for example in themanufacture of sponge rubber articles. The shaped latex is convertedinto a gel or coagulum prior to such steps as drying or vulcanisation.

There are a number of known methods of coagulating or gelling latexcompositions. Thus in the manufacture of articles by the dippingprocess, one well-known method is to coat the outer surface of theformer with a chemical compound, e. g. calcium chloride, having theproperty of coagulating the latex composition. Another known method usedin the dipping process is to add to the latex composition aheat-sensitising agent, namely polyvinyl methyl ether, which causes thecomposition to coagulate at an elevated temperature. In the lattermethod most of the free ammonia present is neutralized. The dipping of aheated former into the heat-sensitised latex composition maintained atroom temperature results in the deposition of a film of rubber on theformer. The use of the heat-sensitising method enables thick deposits tobe built up more rapidly than if coagulant-coated formers are used andalso avoids the danger of destabilising the latex bath by diffusion ofcoagulant from the former. lowever, in the manufacture of dipped goodsit is often necessary for the latex bath to remain stable for longperiods, e. g. for several weeks, and in such cases, it has been foundadvisable to add a stabilising agent to latex compositions renderedheat-sensitive as described above, even though the heat-sensitivity ofthe latex may be reduced thereby.

In the manufacture of sponge rubber articles in which a mould isemployed for shaping the articles, coagulation or gelling has hithertobeen effected by a gelling agent which may be sodium silicofluoride orthe corresponding potassium or barium salt and which is added as asuspension in water to the foamed latex composition prior to pouring thefoamed material into the mould. The action of these known gelling agentsis rapid and hence it is customary to add them after the compoundedlatex has been whipped into a foam so that more time may be availablefor manipulating the fluid latex composition. Even so the time availablefor shaping is strictly limited.

The present invention consists in a rubber latex composition containingas a heat-sensitising agent, a polyoxyalkylene compound having at leastfour oxy-1,2- propylene units in the molecule and having an averagemolecular weight of from 350 to 5,000 and being soluble to the extent ofat least 5% by weight in water at 20 C.

The terms oxypropylene and propylene oxide where used in thisspecification refer in usual manner to the 1,2-propylene compounds andunits derived therefrom formingthe radical -OC2H3(QHs)-.

2,791,567 Patented May 7,

The heat-sensitising agent present in the latex composition of theinvention may most suitably be a polyo'xyallzylene compound having thegeneral formula:

where R and R are similar or dissimilar and are selected from H andalkyl, aryl, alkaryl, aralkyl, alkenyl and acyl radicals containing upto 18 carbon atoms, l

y is not less than 4, and l x may be zero,

the formula indicating the number of oxyalkylene units in the moleculebut not necessarily their sequence rel.- atively to one another.

The heat-sensitising agent may be a polyoxyalkylene compound having aformula similar to that given above, but containing within theoxyalkylene chain an organic residue or diradical of the structure 'ORformed from a di-hydr'oxy compound of the general formula HOR"OH, WhereR is a hydrocarbon radical containing from 4 to 18 carbon atoms, e. g.the diradical formed from 2,4-hexanediol, 1,8-octanediol or 1,3dihydrox'y benzene.

Further, polyoxyalkylene compounds of the kind referred to in the twopreceding paragraphs but having one of the oxygen atoms replaced by asulphur atom may also be-used as heat-sehsitising agents in theinvention.

The amount of heat-sensitising agent present in the comositions of theinvention may vary from about 1% to 10%, and is preferably from 2 to 5%,by weight of the dry rubber content of the composition.

The rubber latex used in the compositions of the invention may beanatural rubber l'atex','but preferably concentrated to to 65% by weightdry rubber content or a mixture of natural rubber latex with a lesseramount of synthetic rubber latex such as that produced by "the emulsionpolymerisation of a mixture of butadiene-lz3 and styrene and knowncommercially as 6R4 latex, the mixture preferably containing from 50 toby weight of dry rubber (natural+synthe'tic). The latex maybe used inthe pre-vulcanised condition, or compounding ingredients may be added toenable vulcanisation to be carried outsubsequen't to 'gelation of thelatex.

The usual, commercially available natural rubber latices areammonia-preserved and have a pH value in the region of 10. Thecompositions of the invention prepared from such latices will have asimilar pH value and when this is the case, the compositions should alsocontain zinc oxide or a similarly acting metal oxide, e. g. magnesiumoxide, which assists the heat s'ensitisation. Zinc oxide is alsonormally added as a vulcanisation activator and will serve both purposeswhen vulcanisable compositions are used. When prevulcanised compositionsare used zinc oxide may have to be added if the-excess, which has beenleft after vulcanisation, proves insutficient. if the composition isrendered substantially neutral, i. e. if its pH value is between'6and'8, then a non-ionic stabilising agent such as cetyl/oleyl alcohol'combined with from 15 to 20 molecules of ethylene oxide should also bepresent in addition to the heat sensitising agent. In the latter case,the presence of zinc oxide or other metal oxide is unnecessary, thoughZinc oxide may still be present as a vulcanisation activator innon-vulcanised compositions and the excess zinc oxide will usually bepresent in prevulcanised compositions. i The heat-sen'sitising agentsused in the latex compositions of the invention have a solubility in 'water which decreases as the temperature is raised and should a enflocculation temperature of betvVeen'ZS" CI and When used for theproduction of articles by the dipping process the heat-sensitising agentshould preferably have a flocculation temperature of between 35 and 55C. When used for the bulk coagulation of rubber in moulds either in abatch or'a continuous process its flocculation temperature shouldpreferably be between 25 and 40 C.

The term flocculation temperature of a compound as used in the presentspecification is the minimum temperature at which a by weight solutionof the compound in water renders standard news type illegible whenviewed in normal daylight through a one inch depth of the solution.

'The flocculation temperature of the heat-sensitiser is an indication ofthe temperature at which a latex composition in which it is incorporatedwill remain stable without coagulation for any appreciable length oftime. Thus to keep the latex compositions of the invention stable theymust be maintained at a temperature below the flocculation temperatureof the heat-sensitising agent used.

The known heat-sensitising agent polyvinyl methyl ether, which haspreviously been used in the dipping process, has a flocculationtemperature of about 30 to 35 C. which may be inconveniently low incertain circumstances, for example, when high atmospheric temperaturesare prevalent. Furthermore, it is difficult to handle as it forms aviscous solution and products resulting from its use have a low wetstrength.

The heat-sensitising agents used in the compositions of'the inventioncan be made of the desired flocculation temperature and solubilitywithout difficulty as will be more fully explained hereinafter and caneasily be handled in aqueous solution. They can also be used in smallerquantities than those recommended for polyvinyl methyl ether andfurthermore no neutralisation of the ammonia present is necessary whenthe latex composition contains zinc oxide or other similarly actingmetal oxide.

Latex compositions in accordance with the invention may be used withadvantage for the production of rubber articles both by the dippingprocess and by the moulding process.

The invention also consists in a process for the manuf-acture of rubberarticles in which a latex composition containing a heat-sensitisingagent in accordance with the invention is shaped, either by dipping ormoulding, and the shaped composition is converted to a gel by heating toa temperature not less than the flocculation temperature of theheat-sensitising agent.

By selectionIof a heat-sensitiser having a suitable floccula'tiontemperature the use of. stabilisers in the dipping process may beavoided when using a composition of the invention having a pH value inthe region of and containing zinc oxide or an equivalent metal oxide,even when the latex bath is in continuous use for several weeks withconstant replenishing of the latex composition. Furthermore, the .heat-sensitisers of suitable flocculation temperature may be added to thelatex composition to be used in the production of sponge rubber articlesprior to foaming the composition since gelling does not occur until thefoam is heated. The process of the invention is accordingly much moreflexible in operation than the known processes.

In one method of carrying out the process of the present invention forthe manufacture of rubber articles by the clipping technique, avulcanisable latex composition having a pH value of about 10 is preparedcontaining a heat-sensitising agent in accordance with the invention.The ingredients of the vulcanisable latex composition will normallyinclude sulpur, a vulcanisation accelerator and from 1 to 2% of zincoxide calculated on the weight of dry rubber content. With this amountof zinc oxide already present, no further zinc oxide need be added, butthe amount of zinc oxide in the vulcanisable latex composition shouldnever be allowed to fall below 0.5% by weight otherwise a markeddecrease in the heat-sensitivity of the latex composition is liable tooccur. The optimum proportion of zinc oxide depends on the compositionof the latex composition, its pH, the conditions under whichvulcanisation is to be carried out and upon the thickness of depositrequired. The optimum proportion of Zinc oxide will normally be between1.0 to 2.0%, calculated on the weight of dry rubber content when the pHof the latex composition is in the range 9.5 to 10.5 and the dry rubbercontent is in the range 55% to 65% calculated on the total weight of thelatex composition. A former of suitable shape and heated to the requiredtemperature is immersed in the latex composition for a time sufficientfor a deposit of the required thickness to be produced, after which theformer is withdrawn and the deposit dried and vulcanised. An immersiontime of about 10 seconds, giving a coating of from 0.015 to 0.030 inch,is quite normal. If a prevulcanised latex composition is used, insteadof the vulcanisable latex composition, no additional vulcanisingingredients will normally be added, except for zinc oxide which againshould be present in an amount preferably not less than 0.5% calculatedon the weight of the dry rubber content.

In another method which may be used for the manufacture of articles bythe clipping process, a prevulcanised latex which has been freed fromany excess of zinc oxide or other metal oxide present and has had its pHvalue reduced to between 6.5 and 8.0 is prepared containing a non-ionicstabilising agent, such as cetyl/oleyl alcohol combined with from 15 to20 molecules of ethylene oxide. and a heat sensitising agent inaccordance with the invention. A heated former is immersed in thecomposition for a time sufficient for a deposit of the requiredthickness to be produced, after which the former is withdrawn and thedeposit dried. The latex may be freed of the metal oxide bycentrifugingand its pH value may be reduced by the addition whilststirring of formaldehyde or dilute hydrochloric acid. The stabiliser isadded to the latex prior to or, preferably, together with the heatsensitising agent as a concentrated aqueous solution. The non-ionicstabiliser may be present in an amount of from 0.4 to 0.9%, andpreferably 0.7%, by weight of the dry rubber content of the composition.

In carrying out the process of the present invention for the manufactureof sponge rubber articles it is preferred to use a composition of thenormal pH, i. e. about 10, containing zinc oxide and no stabilisingagent. In this method one may proceed as follows. The heat-sensitisedlatex composition, having a pH value in the region of 10, is convertedinto a foam of desired volume using, for example, a wire-cage beater.Preferably a foaming agent is also incorporated into the latexcomposition. The foaming agent may be the ammonium or potassium salt ofricinoleic acid, present in an amount between 0.1% and 0.5% on theweight of dry rubber. Alternatively, from 0.1 to 0.4% of amono-octyl-phenyl ether of an octaoxyethylene diol may be used asfoaming agent. After beating the composition into a foam in the mannerdescribed above, the remainder of the compounding i11- gredients,including the vulcanising ingredients, arethen added and the compoundedfoam is poured into a mould of suitable shape. Gelling and vulcanisationof the foam is then carried out in a single operation eithercontinuously or batchwise, preferably by heating the mould and itscontents at C. for a sufiicient period of. time to produce asatisfactory state of vulcanisation, usually be tween 30 and 45 minutes.The vulcanised compound is then washed with water and the excess waterremoved, if desired, by hydro-extraction, the product being finallydried in air at about 40 C. Once again the zinc oxide content shouldnormally be between 1 and 2% calculated on the weight of dry rubbercontent. 7

Consideration will now be given to the factors governing the choice andpreparation of polyoxyalkylene heatsensitising agents for use in thepresent invention.

The flocculation temperature of the heat-sensitising agent may beregarded as the cloud'point ot 'a 5% solution of the agent in water. Asolution containing 2.5% by Weight of the heat-sensi'tising agent willhave a higher cloud point than a by weight solution. Economically it isdesirable to use as small an amount of sensitising agent as possible,and it is preferred to use not more than about 2.5% by weight based onthe dry rubber content of the latex composition. In the preparationanduse of an industrial latex bath variations in the sensitising agentconcentration are liable to occur, sothat it is desirable that the cloudpoint should not differ materially, i. e. by more than about 5 C., fromthe defined flocculation temperature as the sensitising agentconcentration in Water varies between 3% and 7%. It has been found thatthe variation of cloud point with concentration becomes less pronouncedin the case of the polyoxyalkylene compounds of the general formulagiven above as the molecular weight is increased and that such compoundshaving a molecular weight of from 900' to 3000 are satisfactory in thisrespect.

Compounds having the desired molecular weight and flocculationtemperature may be obtained by adjusting the proportions of oxyethyleneand oxypropylene contents in the molecule. Thus by increasing theproportions of oxyethylene groups to oxypropylene groups a compound ofincreased molecular weight can be formed to give a specifiedflocculation temperature. The flocculation temperature appears to besubstantially independent of the structure within a compound of givencomposition.

Particularly satisfactory results and ease of working may be obtainedusing polyoxyalkylene diols as heatsensitising agents, i. e. compoundsof the general formula given above in which both R and R are H.

The attached drawing shows graphically the relationship betweenflocculation temperature and molecular weight for a number of such diolsin which from to 100% by weight of the oxyalkylene groups areoxypropylene groups. The percentage figure at theend of each curve isthe percentage by weight of the oxypropylene content based on the totaloxyalkylene content of the diol to which the curve relates. It hasalready been stated that the flocculation temperature should preferablybe within the range to C. for the dipping process, and

it can be seen from the drawing that for the polyoxyalkylene diol tohave a flocculation temperature within this preferred range and to havealso a molecular weight within the preferred limits of l0003000, thecontent of oxypropylene groups in the diol should be from 50 to 80% byweight of the total content of oxyalkylene groups.

The flocculation temperature of any diol may be reduced by blocking oneor both of its ends by an alkyl, aryl, alkaryl, aralkyl, alkenyl or acylgroup. The degree of the reduction depends on the molecular weight ofthe polyoxyalkylene diol, and more particularly on the molecular weightof the blocking group or groups. Thus when one end H of a diol isreplaced by a group containing from 1 to 4 carbon atoms, e. g. CH3, C4H9or CHsCO, this results in a reduction of 510 C. in the flocculationtemperature. When the end H is replaced by a larger group, e. g.octylphenyl or oleyl, the reduction may be over 100 C. The additionalblocking of the other end of the diol is accompanied by a similarfurther reduction in flocculation temperature together with a reductionin solubility in water at 20 C. For these reasons it is preferred thatin the general formula given above R should be H or an alkyl groupcontaining not more than 4 carbon atoms and that R should be H.

The above factors of composition and structure contrcl the flocculationtemperature of the heat-sensitising agent, but for the sensitising agentto be industrially useful it must be economical and easy to use and mustproduce rubber articles with desirable properties. Theheatsensitisingagent is most easilyihandled as a-2 ):5:0;%' solu+ tion,in water, so that it should desirably-be; soluble in water to thisextent, otherwise handlingrd l qulties are encountered and the latexcomposition becomes diluted unduly with water. Polyoxyalkylene diolscontaining over by weight of oxypropylene groups have ingeneral poorsolubility characteristics. Materials Withboth ends blocked have alsopoorer solubility characteristics than similar but unblocked compounds;For this reason therefore it is preferred to use polyoxyalkylene diolsor their simple mono alkyl ethers (thealkyl radical containing up to 4carbon atoms) containing not more than 80% by weight of oxypropylene.groups.

It is desirable thatthe heat-sensitising agent should have a long bathlife when mixedwith aqueous rubber latex stabilised with ammonia.

This alkaline medium causes hydrolysis of acylated, sensitising agents,so that unless the sensitised latex composition is to be usedimmediately it is preferred not to. use acylated compounds.

Whereas sensitising agents of the desired flocculation temperaturecontaining 5 to 10% by. weight of oxypropylene groups can be prepared bysuitably blocking the ends of polyoxyalkylene diols, such sensitisingagents are not so desirable as those containing a higher proportion ofoxypropylene groups in that they lead to rubber films having little orno wet strength.

Broadly speaking, therefore, the preferred heat-sensitising agent usedin the invention, particularly when the compositions are to be used forthe manufacture of articles by the dipping process, is apolyoxyethyleneoxypropylene diol having a flocculation temperature offrom 35 C. to 55 C., a molecular weight of between 1000 and 2000 and anoxypropylene content of from 50 to 80% by weight, or is a lower alkyl(up to 4C), vinyl or allyl mono-ether of a polyoxyethyleneoxypropylenediol having a flocculation temperature of from 35 to 55 C., a molecularweight of between 500 and 2000 and having an oxypropylene content offrom 40 to 80% by weight.

For the manufacture of sponge rubber articles wherein great bathstability is not required the heat-sensitising agent used maysatisfactorily be a polyoxypropylene diol having a flocculationtemperature of from 25 to 40C. and 'a molecular weight of from 400 to1000.

The polyoxyalkylene heat-sensitising agents focuses in the presentinvention 'can be prepared-by several-known methods all of which involvethe reaction of propylene oxide or ethylene oxide, or mixtures of thetwo, with a suitable hydroxy compound in the presence of a catalyst,usually an alkali metal catalyst. The hydroxy compound may be analcohol, phenol, .oxyor polyoxyrpropylene .diol, oxyor polyoxy-ethylenediol, polyoxyethyleneoxw propylene diol, or mono-alkyl or mono-arylethers of these diols. In the case where the alkylene oxide is onlyethylene oxide, the hydroxy compound should be an oxyorpolyoxy-propylene diol, or polyoxyethyleneoxypropylene diol, or amono-alkyl or mono-aryl etherof such diols.

Such processes inevitably lead to complex mixtures having an averagemolecular weight. slightly less than that predicted from the reactants.It is well known that in addition to wide variation in chain lengtharound the mean, the distribution of individual oxypropylene'andoxyethylene groups in a polyoxypropyleneoxyethylene diol chain of knownaverage composition may vary con.- siderably. Such variations aredescribed in .United States Patent No. 2,425,845 in which diethylcneglycol, for example, is reacted in a batch process with mixtures ofpropylene oxide and ethylene oxide, and in United States Patent No.2,425,755 in which the 'butanol is reacted in like manner. possessingsuitable flocculation temperatures and rah-suitable solubilitiesproduced by these processes 'are useful It has been found that materials7 heat -sensitising agents. Thus the polyoxyethyleneoxypropylenecompounds marketed by Carbide and Carbon Chemicals Corporation as Uconlubricants of the H. B. series have been found to be usefulheat-sensitising agents. They are believed to be monobutyl ethers ofpolyoxyethyleneoxypropylene diols containing approximately equal weightsof oxyethylene and oxypropylene groups, and have average molecularweights of from 500 to 3000.

Suitable polyoxyethyleneoxypropylene diols, or their mono-alkyl ormono-aryl ethers, for use as heat-sensitising agents in the inventionmay be prepared by continuousiy passing a mixture of ethylene oxide andpropylene oxide in homogeneous admixture with the appropriate organichydroxy compound through a reactor maintained at a temperature between50 and 190 C. as described in British Patent No. 757,309, correspondingto United States application Serial Number 350,663, filed April 23,1953. The products resulting from this process have a concentration ofoxyethyiene groups away from, and of oxypropylene groups towards thefree ends of the chains.

Further suitable polyoxyalkylene compounds Eor use in the presentinvention may be produced by reacting an hydroxy compound containingoxypropylene groups with ethylene oxide as described in British PatentNo. 736,991, corresponding to United States application Serial Number279,768, filed April 1, 1952, or by reacting an hydroxy compound inwhich oxyethylene groups are present with propylene oxide, as describedin British Patent No. 757,- 309. These two processes are continuousprocesses, but products of similar composition may be prepared from thesame reactants by the known batch processes. Polyoxypropylene diols, ortheir mono-alkyl or mono-aryl others may also be used in the invention.The polyoxypropylene diols have been Widely described and are eitheravailably commercially or may be prepared by standard methods.

Mixtures of any of the polyoxyalkylene compounds referred to above assuitable for use in the invention, with one another or with the vinyl oralkyl ethers produced during the course of their manufacture may also beused as heat-sensitising agents in the invention.

Following are examples illustrative of the invention, preceded bydetails of the various heat-sensitiscrs used therein.

All parts and percentages given below are by weight.

Definitions of various terms and abbreviations used in describing theheat-sensitisers and in the examples are as follows:

H. S.: An abbreviation for heat-sensitiser.

Z. D. C.: An abbreviation for zinc diethyldithiocarbamate, avulcanisation accelerator.

Oxypropylene Content: The weight percentage of oxypropylene groups inthe H. S. Thus, if the formula of the H. S. is represented as R(OC2H4) n(OCaHs) mOH the oxypropylene content will be (5800111) /(58m+441t+M)Where M is the molecular weight of ROH.

Acetyl M. Wt.: The molecular weight determined by reaction with amixture of acetic anhydride and pyridine.

Calculated M. Wt.: The molecular Weight calculated from the materialsreacted.

Viscosity Index: The viscosity index as determined by method IP-73/ 47described in the book Standard Methods for Testing Petroleum and itsProducts published in 1949 by the Institute of Petroleum, London.

Pour Point: The pour point as determined by method IP-l5 42 in the bookreferred to above.

Bromine No.: The weight in grams of bromine absorbed per 100 grams ofproductas determined by the Francis method.

H. S. l, H. S. 2, H. S. 4, and H. S. 6 were produced by the processdescribed in British Patent No. 757,309.

In the production of H. S. l, a mixture of propylene oxide and ethyleneoxide was reacted with a polyoxypropylene diol of molecular weight 370to yield a product which was predominantly a polyoxyethyleneoxypropylenediol having the characteristics shown in the accompanying table.

In the production of H. S. 2, a mixture of propylene oxide and ethyleneoxide was reacted with diethylene glycol to yield a product which waspredominantly a polyoxyethyleneoxypropylene diol having thecharacteristics shown in the accompanying table.

In the production of H. S. 4, propylene oxide was reacted with themono-methyl ether of ethylene glycol to yield a product which waspredominantly the monomethyl ether of a polyoxyethyleneoxypropylenediol, which ether had the characteristics shown in the accompanyingtable.

In the production of H. S. 6, propylene oxide was reacted withdipropylene glycol to yield a product which was predominantly apolyoxypropylene diol having the characteristics shown in theaccompanying table.

H. S. 3 was produced by the acetylation of H. S. 2 with excess aceticanhydride followed by purification. It had a flocculation temperature of33 C.

H. S. 7 was prepared in known manner from H. S. 6 by feeding ethyleneoxide slowly into a stirred mass of H. S. 6 containing in solution acatalytic amount of caustic soda and maintained at a temperature of from120- 130 C. The product was predominantly a polyoxyethyleneoxypropylenediol having the characteristics shown in the accompanying table.

H. S. 9 was prepared by the process described in U. S. Patent No.2,425,755. Butanol containing dissolved sodium metal was heated to itsboiling point and a mixture of equal parts of ethylene oxide andpropylene oxide was then fed slowly to the butanol. As the reactionproceeded the temperature was gradually raised to 130 C. The mixture ofalkylene oxides was added as a liquid through a reflux condenser. Theproduct was predominantly the monobutyl ether of apolyoxyethyleneoxypropylene diol, which ether had the characteristicsshown in the accompanying table.

H. S. 10 was prepared in known manner by feeding propylene oxide slowlyto a polyoxyethylene diol of average molecular weight 400 containing acatalytic amount of sodium metal in solution and maintained at atemperature of 120130 C. The product was predominantlypolyoxyethyleneoxypropylene diol having the characteristics shown in theaccompanying table.

H. S. 5, and H. S. 8 were commercially available products. H. S. 5 was apolyoxypropylene diol of stated molecular weight 400 and having thecharacteristics shown in the accompanying table. H. S. 8 waspredominantly the monoalkyl (believed to be butyl) ether of apolyoxyethyleneoxypropylene diol (Ucon lubricant -HB260) which ether hadthe characteristics shown in the accompanying table.

The physical properties given in the accompanying table of heatsensitisers H. S. l, 2, 4, 6, 7, 9, and 10 produced as described above,were determined after purification in the following manner.

The crude reaction product was heated to 100 C. at 20 mm. pressure toremove unreacted alkylene oxidesv It was then dissolved in water andcarbon dioxide was bubbled through the solution until it was neutral.The resulting aqueous solution was then heated to to C. and sodiumsulphate added, if necessary, to assist separation of the mixture intoan upper product layer and into a lower aqueous layer. The latter layerwas removed and the product layer was washed twice with aqueous sodiumsulphate at 90 to 95 C. and separated while hot from the aqueous phase.The product was then heated to to C. at 20 mm. pressure to remove tracesof dis solved water and filtered while hot to remove inorganic 9 saltswhich had beeii present ififslu'ti the of water. The various refinedproducts v ed nun waterwhite to pale yellow liquids, p p 7 The heatsensitisers H. S. 1, 2,- 4, 6, 7, 9, and 10 pro duced as described abovewere found to give satisfactory results when used after purification asdescribed in the preceding paragraph and also when the renewingtreatmerit was substituted for this purification process. a p

The crude reaction product was heated to 100 C. at 20 pressure to removeunreacte'd alkyleii'e oxides. It was then dissolved in water andneutralized with sulphuric acid The neutral aqueous solutioh usuallycontaining 25 or 50% of heat 'sensi ti'ser was usd without furthertreatment in the following examples.

The heat sensitisers H. S. ai'iii. 8 were used in the form bought. Theirphysical characteristics were de trmined in this form.

98 C. oiids and th'deposit rotated was afield 311a v lcamsed asdescribed in Example 1. Theisiiltin'g rubber mar had a uniform thicknessof 0.048 inch and could be stripped easily from the former.

EXAMPLE 3 The following ingredients were added to 166 parts of acommercial, prevulcanis'ed latex (pH 10.2) of natural TABLE Propertiesof hiirzf S''iisifizei's used iii Example 1, 2 and 4 to 14 H.S1 H.s.2H.S.4 11.85 as... H.S.7 use H.S.9 H.S.10

Calculated M'. Wt 1, 100 1,260 450 940 1, 030 700 1,100 Acetyl M 7V1: T1, 330 90 300 370 720 1, 000 980 550 898 Oxypropylerie content, percent-59 82 85 96 98 71 46 45 G4 Flocculation Temperature, O. 49 40 40 58 ,2830 51 52 51. 5 Density at ,C.. gJml 1. 040 1. 024 1. 004 1 01 0. 997 1.029 1. 035 1. 031 1. 048 Bromine No., g./100fg 1. 9 1. 5 5. 7 0. 0. 7 p0.9 2.4 Refractive Index. 17.1, 1. 456 1. 453 1. 443 1. 448 1.5156 1.452 1. 457 Viscosity at 100 F; centistoke's- 112 76. .5 16.1 32. 6 47. 7110 56. 2 32. 6 115 Viscosity at 210 F centistok'e's 17.2 11. ,3 3. 404. 44 7. 3 13. 9 11. 3 6. 63 17. 9 Viscisity Index. 139 132 80 2 121 124154 153 139 Pour Point, F 45 -60 -40 -45 +85 40 -60 +5 (Melting Point)sol r 3 water at 20 0., Infinite Infinite Infinltb Infinite 130 InfiniteInfinite Infinite Infinite Emma i Ammonia-preserved, natural rubberlatex (p11 10.5 of 60% dry rubber content compounded with the Thesulphur, zinc oxide and Q. were add ed as a 50% dispersion in water, andthe heat-sensitising agent H. S. 1 as a solutioii in water. I

A cylindrical aluminium rennet of 1 inch altimeter was heated in an ovento 80 C. aiid then imine d in the above latex composition for 10secofi'ds with gentle stirring of the latex, whereby a smooth film offirmly gelled latex was deposited on the former. The apesit was dried at40 C. and then vulcanise'd by heatihg in an oven at 100 C. for half anhour. The rubber film so prepared had a uniform thickness of 0.022 ihch.In an otherwise identical test in which H. S. 1 was omitted from thelatex compound, no film 0f gelled latex wasuepusited on the former. Theheat-sensitised latex composition desci'ibed above, after being storedin a closed vessel at 'C. for three weeks, showed no signs of gelationor coagulation.

EXAMPLE 2 The following latex composition ,was prepared usingammonia-preserved, natural rubber latex (pH 10.5) con taining 60% rubberby weight:

The above ingredients were compounded as in Example 1. A cylindricalformer of 1 inch diameter heated to rubber marketed by Revertex Limitedunder the trade name Revultex" aiid containing 60% rubber.

Parts Zinc oxide; 2.0 H. S. 1 2.5

v p Pam Natural rubber latex (60% rubb'e i 166 Lls sapl N H. S. 1 2.5Zinc oxide 2.5

Sulphur 1.5 Z. D. C 0.5

Lissapol N, -which was employed in the above compo- 'si'tio'fi as arunning agent; is a commercial surface active agent marketed ImperialGheilnical lndustries Limited and believed to be an a aeeut solution ofa monoalkaryl ether of a polyethylene glycol.

The rubber latex, Lissapbl N and H. S. 1 (as a 20% aqueous solution)were first whipped into a foam of volume approximately 6 times theirnormal volume by means of a wire cage beater, after which the zincoxide, Sulphur and Z. D; 6. were added together as a 50% dispersion inwater with continued Whipping of the latex The foam so formed was pouredinto cylindrical moulds 2 /2 inches in diameter and 2. inches ,deep. Themoulds were then heated in an air oven. at C. for 40 minutes,

' 11 thereby effecting gelation and vulcanisation of the compound. Theresulting product was then removed from the mould, washed in runningcold water for 2 hours and finally dried in an air oven at 40 C. Thesponge so produced was cut open and was found to have a line, uniformpore structure.

Parts Natural rubber latex (60% rubber) 116 Butadiene styrene eopolymerlatex (40% copolymer) 75 Sulphur 1.5 Zinc oxide 2.5 2. D. C 0.75 H. S. l2.5

The above ingredients were mixed as described in Example 1. Acylindrical aluminium former of 1 inch diameter heated to 90 C. wasimmersed in the latex compound for 10 seconds and the resulting depositwas dried at 35 C. Vulcanisation was effected by heating for 60 minutesat'100" C. The deposit formed was found to be 0.032 inch thick.

EXAMPLE 7 The following ingredients were formed into a latex compositionusing the natural rubber latex referred to in Example 2:

7 Parts Natural rubber latex (60% rubber) 166 Sulphur 1.5 Zinc oxide 2.5Z. D. C 0.5 H. S. 4 3.0

The above ingredients were compounded as in Example 1. A cylindricalaluminium former of 1 inch diameter heated to 98 C. was immersed in thelatex compound for 10 seconds and the deposit was then dried andvulcanised as in Example 1. The resulting rubber film had a uniformthickness of 0.030 inch.

EXAMPLE 8 A latex composition was prepared as in Example 1, with 2.5parts of H. S. 5 in place of the 2.5 parts of H. S. l.

The resulting latex composition yielded upon an aluminium former of 1inch diameter treated as described in Example 1, a rubber film having auniform thickness of 0.020 inch which would be stripped easily from thefonner.

EXAMPLE 9 A latex composition was prepared as in Example 1, with 2.5parts of H. S. 6 in place of the 2.5 parts of H. S. 1.

The resulting latex composition yielded upon an aluminium former of 1inch diameter treated as described in Example 1, a rubber film having auniform thickness of 0.025 inch which could be stripped easily from theformer.

EXAMPLE A latex composition was prepared as in Example 1, with 2.5 partsof H. S. 7 in place of the 2.5 parts of H. S. 1.

The resulting latex composition yielded upon an aluminium formerof 1inch diameter treated as described in Example 1, a rubber film having auniform thickness of 0.023 inch which could be stripped easily from theformer. a 1 a A product similar in physical characteristics'andheatsensitising properties to H. S. 7 was also made by reacting ethyleneoxide continuously with H. S. 6 by a process as described in BritistPatent No. 736,991.

EX AMPLE 11 A latex composition was prepared as in Example 1, with 2.5parts of H. S. 8 in place of the 2.5 parts of H. S. 1.

The resulting latex composition yielded upon an aluminium former of 1inch diameter treated as described in Example 1, a rubber film having auniform thickness of 0.020 inch which could be stripped easily from theformer.

EXAMPLE 12 A latex composition was prepared as in Example 1, with 2.5parts of H. S. 9 in place of the 2.5 parts of H. S. 1.

The resulting latex composition yielded upon an aluminium former of 1'inch diameter treated as described in Example 1, a rubber film having auniform thickness of 0,020 inch which could be stripped easily from theformer.

' EXAMPLE 13 A latex composition was prepared as in Example 1, with 2.5parts of H. S. 10 in place of the 2.5 parts of H. S. 1.

The resulting latex composition yielded upon an aluminium former of 1inch diameter treated as described in Example 1, a rubberfilm having auniform thickness 'of 0.023 inch which could be stripped easily from theformer.

A product similar in physical characteristics and heatsensitisingproperties to H. S. 10 was also made by reacting propylene oxidecontinuously with polyoxyethylene die] of average molecular Weight 600by a process as described in British PatentNoJ 757,309.

EXAMPLE 14 The following ingredients were formed into a latexcomposition using the natural rubber latex referred to in Example 2:

The foaming agent, ammonium ricinoleate, was added in the form of a 25%solution in water and the heatsensitiser H. S. 7 was added as a 20%solution in water. The rubber latex, foaming agent and heat-sensitiserwere first whipped together intoa foam of a volume approximately sixtimes their normal volume using a wire cage beater, after which the zincoxide, sulphur and Z. D. C. were added together as a 50% dispersion inwater, with continued whipping of the latex mix. The foam was thenconverted into sponge rubber articles in the manner described in Example5. The resulting products had a fine and uniform pore structure.

EXAMPLE 15 The following ingredients were formed into a latexcomposition using the natural rubber latex referred to in Example 2'.

a The foaming agent (ammonium ricinoleate) and the heat-sensitiser wereadded to the latex as 25 solutions in water, The mixture was whippedinto a foam approximately four times the original volume and the su1phur, zinc oxide and Z. I). C. then added as a 50% dispersion in waterwith continued whipping. The foamed mixture was then converted intosponge rubber articles as described in Example 5. The resulting productshad a fine and uniform pore structure with a bulk density approximately0.18 gm./ cc.

EXAMPLE 16 The following ingredients were formed into a. latexcomposition for the preparation of sponge rubber articles of bulkdensity approximately 0.08 gm./ cc.

Parts Natural rubber latex (60% rubber) 166 H. S. 6 8 Zinc oxide 1.5Sulphur 1.5 Z. D. C 1.5

The latex and heat sensitiser (the latter as a 25% aqueous solution)were mixed together and whipped into a foam of approximately nine timesthe original volume of latex. The vulcanising ingredients were thenadded together as a 50% dispersion in water, with further whipping.Moulding, vulcanisation and drying were carried out as described inExample 5. The resulting sponge articles were found to have a fine evenpore structure and bulk densities of approximately 0.08 gm./cc.

EXAMPLE 17 The following ingredients were formed into a latexcomposition using the natural rubber latex referred to in Example 2.

Parts Natural rubber latex (60% rubber) 166 H. S. 6 2.5 Cetyl alcoholcondensed with 17 mols ethylene oxide 0.7 Hydrochloric acid aqueoussolution by weight 33 Zinc oxide 1.0 Sulphur 1.0 Z. D. C 1.0

In this example the polyoxypropylene diol and the cetyl alcohol/ethyleneoxide condensate were added to the latex together as a 25% aqueoussolution. The aqueous hydrochloric acid was then added with stirringwhereby the pH of the latex bath was reduced to 7.0202. The vulcanisingingredients were then added. On dipping a heated aluminium former at 70C. into this bath a firmly gelled deposit of rubber was produced whichwas dried and vulcanised as described in Example 1 and was then easilystripped from the former.

We claim:

1. A rubber latex composition containing as a heatsensitizing agent apolyoxyalkylene compound which has an average molecular weight ofbetween 350 and 5000, is soluble to the extent of at least 5% in waterat 20 C and is of the general formula where R is selected from the groupconsisting of H and alkyl and alkenyl radicals containing not more than4 carbon atoms, x is selected from the group consisting of zero and aninteger and y is an integer of at least 4.

2. A rubber latex composition as claimed in claim 1, in which the rubberlatex is a natural rubber latex of pH from about 9.5 to about 10.5 andthe composition contains zinc oxide.

3. A rubber latex composition as claimed in claim 1, in which the rubberlatex is a mixture of natural rubber latex and a lesser amount ofsynthetic rubber latex obtained by emulsion copolymerization ofbutadiene and styrene.

4. A rubber latex composition as claimed in claim 2, in which saidpolyoxyalkylene compound is a polyoxyethyleneoxypropylene diol which hasan average molecular weight between 900 and 2000, has an oxypropylenecontent of from 50 to by weight and is soluble to the extent of at least20% by weight in water at 20 C.

5. A rubber latex composition as claimed in claim 2, in which saidpolyoxyalkylene compound is a polyoxypropylene diol which has an averagemolecular weight between 400 and 1000.

6. A rubber latex composition as claimed in claim 2, in which saidpolyoxyalkylene compound is a monoether of a polyoxyethyleneoxypropylenediol which has an average molecular weight between 500 and 2000, anoxypropylene content of from 40 to 80% by weight and is soluble to theextent of at least 20% by weight in water at 20 C.

7. In the manufacture of rubber articles by the shaping and the gellingby heating of a prevulcanized rubber latex composition, the step whichcomprises rendering the composition heat sensitive prior to gelling bythe addition thereto of: a polyoxyallrylene compound which has amolecular weight between 400 and 2000, is soluble in water at 20 C. tothe extent of at least 20% by weight, and is of the general formulawhere R is selected from the group consisting of H and alkyl and alkenylradicals containing not more than 4 carbon atoms, y is an integer of atleast 4, and x is an integer.

8. In the manufacture of rubber articles by shaping a natural rubberlatex composition containing a. plurality of vulcanizing ingredientsincluding sulfur, a rubber vulcanization accelerator and Zinc oxidefollowed by gelling by heating of the composition and vulcanizing thegel so formed, the step which comprises rendering the composition heatsensitive prior to gelling by the addition thereto of a polyoxyalkylenecompound which has a molecular weight between 400 and 2000, is solublein water at 20 C. to the extent of at least 20% by weight, and is of thegeneral formula where R is selected from the group consisting of H andalkyl and alkenyl radicals containing not more than 4 carbon atoms, y isan integer of at least 4, and x is an integer.

9. A process for the manufacture of sponge rubber articles whichcomprises preparing a compounded natural rubber latex foam having a pHvalue of about 10 and containing a plurality of vulcanizing ingredientsincluding sulfur, a rubber vulcanization accelerator and zinc oxide and,as a heat-sensitizing agent, a polyoxypropylene diol of molecular weightbetween 400 and 900 and soluble in water at 25 C. to the extent of atleast 5% by weight, shaping the foam, heating the shaped foam to atemperature not less than that at which the said diol becomes less than5% soluble by weight in water and vulcanizing the gel thus formed.v

References Cited in the file of this patent UNITED STATES PATENTS2,215,562 Ogilby Sept. 24, 1940 2,442,341 Bufiington June 1, 19482,534,375 Rumbold Dec. 19, 1950 2,587,279 Bevilacqua Feb. 26, 19522,598,127 Keckler May 27, 1952 FOREIGN PATENTS 470,181 Great BritainDec. 31, 1936 624,917 Great Britain June 17, 1949

1. A RUBBER LATEX COMPOSITION CONTAINING AS A HEATSENSITIZING AGENT APOLYOXYALKYLENE COMPOUND WHICH HAS AN AVERAGE MOLECULAR WEIGHT OF BETWEN350 AND 5000, IS SOLUBLE TO THE EXTENT OF AT LEAST 5% IN WATER AT 20*C.,AND IS OF THE GENERAL FORMULA